1. Field of the Invention
The present invention relates to a semiconductor apparatus and a temperature detection circuit, and, particularly, to a semiconductor apparatus including a power transistor that outputs a large current and a temperature detection circuit.
2. Description of Related Art
Recently, a power transistor has been often used in power control of a controlled circuit that consumes a large current. The controlled circuit is a motor or the like, for example. In a power transistor that is used in such applications, heating of a device is prevented by lowering resistance during conduction and letting several tens of amperes of current flow. However, when anomaly occurs in the controlled circuit, an excessive current which is larger than a normally expected current flows, which causes heating and breaking of the power transistor. To avoid this, a power supply circuit that uses a power transistor turns off the power transistor upon occurrence of overheating in the power transistor, thereby preventing thermal breakdown of a device. A temperature detection circuit is used as a protection circuit against overheating.
Examples of such a protection circuit are disclosed in U.S. Pat. No. 6,046,470 and Japanese Unexamined Patent Application Publication No. 06-232410. A protection circuit 100 disclosed in U.S. Pat. No. 6,046,470 is described firstly. FIG. 8 shows a circuit diagram of the protection circuit 100. As shown in FIG. 8, the protection circuit 100 detects the overheated state of a MOSFET 110 and setting a signal VOUT to High level. In the protection circuit 100, a forward bias voltage Vbe is generated by making a current Ibias from a current source 101 flow from an anode to a cathode of a diode D2. In the protection circuit 100, the forward bias voltage Vbe is amplified by an amplifier 102. Then, the amplified forward bias voltage Vbe is compared with a reference voltage VREF in a comparator 103, thereby determining a logical level of the signal VOUT. The forward bias voltage Vbe has characteristics that vary with temperature. Thus, the protection circuit 100 detects the overheated state of the MOSFET 110 by detecting that the forward bias voltage Vbe falls below a predetermined voltage.
FIG. 9 shows an equivalent circuit of a MOS semiconductor device 200 disclosed in Japanese Unexamined Patent Application Publication No. 06-232410. In the MOS semiconductor device 200, a MOS transistor 210, a diode 220 that detects the temperature of the MOS transistor 210 and a resistor 230 are formed on one semiconductor substrate. In the MOS semiconductor device 200, the diode 220 and the resistor 230 are connected in series between the gate and the source of the MOS transistor 210. The cathode of the diode 220 is connected to the gate of the MOS transistor 210, and the anode of the diode 220 is connected to the source of the MOS transistor 210. Further, the resistor 230 is connected between the cathode of the diode 220 and the gate of the MOS transistor 210. In the MOS semiconductor device 200, when a gate voltage is applied to the MOS transistor 210, a reverse voltage is applied to the diode 220. The backward leakage current in the diode 220 increases with the temperature rise of the semiconductor substrate, and upon reaching a predetermined temperature, the logical level of a detection signal So that is output from a node between the resistor 230 and the diode 220 changes from High level to Low level. In the MOS semiconductor device 200, a voltage draw-out circuit is made to operate from a gate terminal according to the logical level of the detection signal So, thereby protecting the MOS transistor 210 from overheat breakdown.